1. Field of the Invention
The present invention relates generally to the field of acoustic scanning and, more specifically, to a calibration block system and method for calibration of acoustic transducers.
2. Description of the Background
Calibration blocks for calibrating acoustic transducers are well known. However, the inventors believe that prior art calibration blocks have many problems that result in difficult to solve calibration problems. These problems limit the potential effectiveness of acoustic, e.g., ultrasonic, transducers such as phased array acoustic transducers. The term “phased array” when used herein refers to phased array acoustic, e.g., ultrasonic, transducers.
In principle, phased array acoustic transducers should have important advantages over other non-destructive means to test welds. Phased array transducers may utilize multiple elements for quickly scanning material to be investigated from multiple angles. At least theoretically, phased array acoustic transducers should provide additional information as compared to other nondestructive means to test welds that should allow the user to obtain a much clearer picture of a feature such as a weld. An x-ray, for example, does not provide enough information to obtain a detailed 3-D picture of the internal features of the weld. Unfortunately, at least in the prior art, the accuracy and repeatability of phased array transducers is a significant problem. When attempts are made to utilize other types of transducer measurements in conjunction with phased array acoustic transducers, additional significant problems may arise.
Phased array acoustic transducers are highly sensitive to orientation. For instance, one or more of signal amplitude, signal velocity, and/or wedge delay information might be affected. Thus, the phased array output information is susceptible to significant variations with very slight changes in orientation. Ironically, the same sensitivity and amount of information, which is an advantage of phased array transducers, has also been a problematic disadvantage. Moreover, such systems tend to be very expensive, dedicated to a specific scanning purpose, and not readily adaptable to different scanning purposes. These problems and the high cost of such systems have limited their practical value for scanning welds.
In the prior art, when multiple phased array transducers are utilized, each transducer may be calibrated by orienting the transducer with respect to defects or features having a known geometry or structure. However, because the phased array transducers are so sensitive to their orientation, one or more of the orientations of the transducers may change as compared to that used during calibration. To attempt to determine which of multiple transducers is no longer calibrated correctly is difficult, time consuming, and ultimately may not be possible even after hours of work.
When attempting to combine outputs from different types of acoustic transducers, it has been difficult to match the readings. For instance, time of flight transducers may not be mounted in such a way that they are set to view the same features as a phased array transducer.
Good calibrations require the ability to repeat physical movement of the transducers with respect to known embedded features under conditions that do not change. Prior art calibrators and calibration techniques frequently introduce numerous variables into calibrations. These errors may include variations in the orientation of one or more of multiple phased array transducers, variations in acoustic couplant, variations in the encoder measurements, and other calibration variations, which ultimately result in an inconsistent testing of tubular welds.
When scanning large diameter tubulars, due to the time and cost of making welds, it is important that the means for verifying/certifying the weld is repeatable and accurate. Only in this way can welding techniques be developed that produce a consistently quality weld and reliable proof that the weld is acceptable for its intended purpose. Exemplary examples of large diameter welding machines, complex pipe/connector weld joints, methods of welding, and welding alignment devices are shown in US Publication No. 20060191874, to R. L. Holdren, entitled Pipe/Connector Weld Joint, And Methods Of Welding Same, and US Publication No. 20050087581, to Otten et al., entitled Welding Alignment Device, and Methods of Using Same, both publications assigned as is the present application, and both publications being hereby incorporated herein by reference for all purposes.
Consequently, there remains a long felt need for improved methods for calibration systems starting with an improved calibration block that provides more reliable and accurate acoustic transducer calibration. Those skilled in the art have long sought and will appreciate the present invention, which addresses these and other problems.